Pilot studies indicate that an immunoassay method based on an electroactive label which is detectable by an electrochemical technique such as polarography or voltammetry is feasible. These studies utilized estriol as a model system with mercuricacetate as the electroactive label and differential pulse polarography as the method of detection. Estriol antibody was found to reversibly bind with the labeled estriol. Separation of bound from unbound labeled estriol was unnecessary since the two forms are electrochemically distinguishable. The wide dynamic range and low detection limits of modern electroanalytical techniques such as thin-layer differential pulse voltammetry and stripping voltammetry make labeling the antigen with an electroactive group a potentially useful approach to immunoassay methodology. The elimination of radioactive materials and the need to separate bound from unbound antigen are the main benefit to be gained. A variety of electroactive labels (mercuricacetate, iodide, ruthenium, bifunctional chelating agents for metal ions, and double antibody systems) will be evaluated on systems such as estriol, insulin, prolactin, IgG, thyroxine (T4) and 3,5,3'-triiodothyronine (T3). The electrochemical techniques of differential pulse polarography, thin-layer differential pulse voltammetry and stripping voltammetry will be evaluated to determine which technique is most readily adaptable to a particular assay. How detection limits compare with other techniques, especially radioimmunoassay will be determined for selected systems. The effect of electroactive labels on antibody affinity will be evaluated. The generality of not needing to separate bound from unbound antigen will be explored with several systems. These studies will serve as the basis for the further development of immunoassay procedures for the determination of specific compounds for which the use of an electroactive label is advantageous over existing procedures.